Researchers investigated soya in the diet

The humble soya bean may play a role in the problem of male infertility, a team of researchers in Belfast has found.

Soya contains the female hormone oestrogen and too much of it is being linked to poor quality sperm.

Dr Lorraine Anderson says she found the link in research carried out at the Royal Victoria Hospital in Belfast.

"What many men do not realise is that soya is not just consumed by vegetarians, it is contained in a lot of everyday processed foods.

"It is contained in foods such as pizzas, any of those foods that you add hot water to, to reconstitute them, or some of the pre-packaged dinners like steak and kidney pies," Dr Anderson said.

If men are consuming large amounts of soya products, for example, there is a negative relationship between that and the quality of their sperm Dr Sheena Lewis Queen's University, Belfast

"You'll find that a lot of the meat is not really meat, it is soya protein because it is cheaper and soya has the highest percentage of oestrogens compared to any other foods."

The director of reproductive medicine at Queen's University, Belfast, Dr Sheena Lewis, said the findings were clear.

"What we have shown is that if men are consuming large amounts of soya products, for example, there is a negative relationship between that and the quality of their sperm.

"If they already have a slight problem in that area, then it might be better for them not to consume so much."

Dr Lewis said that the way to avoid excess oestrogen was to eat fresh produce.

"In our fast food diets, we are inclined to eat lots of meals and we really don't know what the ingredients are," she said.

"If we eat fresh fruits, if we make fresh food at home ourselves, which I know is very difficult in today's busy lifestyle, then we are really aware of what the ingredients are."

However, the research does not simply have implications for men who wish to start a family.

Dr Anderson said if boys eat a lot of soya when they are growing up, it can damage their reproductive capability.

"The key time for that is when a male foetus is developing and in the early toddler years and up to puberty.

"All through that period, if you alter the oestrogen that a man is exposed to, you can not only affect their sperm quality but affect the development of their reproductive tract, so that you can get an increase in structural abnormalities like undescended testes and you can also get other problems later in life, such as testicular cancer."